Conventionally, as illustrated in FIG. 11, a coil is known in which unit coil portions 9 formed by spirally winding a conductive wire 94 are repeatedly placed side by side in a winding axis direction.
As a method of manufacturing such a coil, there is known a method of continuously forming a first unit wound portion 91, a second unit wound portion 92, and a third unit wound portion 93 having mutually different inner circumferential lengths in a winding axis direction by spirally winding a conductive wire as illustrated in FIG. 12A, and continuously forming unit coil portions formed of the pluralities of unit wound portions 91, 92, 93 in the winding axis direction, thereby manufacturing an interim product of an air core coil, and then, compressing the interim product in the winding axis direction, pushing in at least a part of the second unit wound portion 92 inside the third unit wound portion 93, and pushing in at least a part of the first unit wound portion 91 inside the second unit wound portion 92 as illustrated in FIG. 12B, thereby obtaining a finished product of the air core coil formed of a plurality of coil layers (three layers in the example of the figure), (Patent Document 1).
In a transformer for large power and high voltage, as illustrated in FIG. 10, a large coil 8 formed by winding a conductive wire having a coated surface and a rectangular cross-section in multiple layers or a large coil (not shown) formed by lap winding a thin resin film and a wide sheet metal in multiple layers and further increasing the number of turns per row is conventionally used as a primary winding or a secondary winding.
In manufacturing processes of such a coil, as illustrated in FIG. 10, many coil units 81 spirally wound from an inner circumferential side toward an outer circumferential side are manufactured first, and then, the coil units 81 are arrayed in a winding axis direction, and the adjacent coil units 81, 81 are connected in series to each other by a connecting wire (not shown).